Expedient restoration of flow is necessary to avoid grave hemodynamic consequences in patients who are already refractory to maximum inotropic and vasopressor therapy, as well as organ ischemia and circuit thrombosis. Nevertheless, although this is a safety feature, stopping the ECMO circuitry and therefore the blood flow may be followed by deleterious consequences such as hypotension or the occurrence of thrombi.Īlthough the administration of contrast agents has been deemed safe, we have had two instances at our institution in which the peripheral administration of a microbubble contrast agent, namely, Definity (perflutren lipid microsphere Lantheus Medical Imaging, North Billerica, MA) during contrast transthoracic echocardiography resulted in activation of the ECMO bubble detector alarm and subsequent engagement of zero-flow mode, resulting in hemodynamic instability. This safety feature is designed to prevent deleterious cardiovascular and neurologic sequelae associated with air embolism during ECMO. This mode applies sufficient revolutions per minute to prevent backflow from the arterial cannula into the venous cannula and prevents forward flow as well, hence the name zero-flow mode. If the alarm is not overridden within 6 sec, “zero-flow mode” is engaged. Activation of the bubble detector results in an alarm, followed by pump shutdown. The ECMO system used at our institution (CARDIOHELP MAQUET Medical Systems USA, Wayne, NJ) has an integrated sensor that uses ultrasound to detect changes in flow dynamics associated with the presence of air bubbles or thrombi >5 mm in dimension.
This information is used clinically to determine whether to wean patients from ECMO support. It is common practice to use contrast transthoracic echocardiography to improve the visualization of endocardial borders and allow more accurate assessments of ventricular function. Acute disruption of forward flow in ECMO-dependent patients will result in severe hypoperfusion and must be avoided at all costs. Patients requiring venoarterial ECMO are, by definition, on the verge of cardiopulmonary collapse. Venoarterial extracorporeal membrane oxygenation (ECMO) is a temporizing therapy for patients with refractory cardiogenic shock, and it may also be a bridge to destination therapy or cardiac transplantation.
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